Impact of biofibers and coupling agents on the weathering characteristics of composites

This paper explores the ultraviolet (UV) weathering performance of high density polyethylene (HDPE) composites with different biofiber fillers and coupling agent. Biofiber polymer composite (BFPC) material samples were prepared using oak, cotton burr and stem (CBS) or guayule bagasse as fiber source HDPE as resin, and two different coupling agents. Weathering variables included exposure to UV radiation and moisture cycles for up to 2200 h. Each variable can degrade BFPC matrix independently or synergistically. The impact of weathering was measured through the changes in the surface matrix, mechanical properties and thermal stability of BFPC as a function of biofibers types and coupling agents. The coupling agent treated composites showed color shift (ΔE) and variable surface degradation. Water absorption of the weathered samples continued to increase after 10 days of immersion. Flexural stiffness, strength and impact properties of weathered samples decreased regardless of fiber type or coupling agent. Minimal linear thermal expansion was noted in weathered composites with coupling agents. Overall coupling agent helped to retain the mechanical properties of composites after exposure to UV weathering.